This invention relates to deicing devices and methods, and particularly, to deicing devices and methods employed in aerodynamic bodies or components.
Aircraft are commonly subjected to operating conditions in which ice may accumulate on certain surfaces. Accumulated ice may interfere with performance of some surfaces, and, in the case of some aircraft components, may completely block proper operation.
Examples of aircraft components that are adversely affected by even small accumulations of ice include pitot tubes and total temperature probes. Total temperature probes, for example, commonly include an aerodynamically shaped probe housing with an inlet scoop mounted at one end and a temperature sensor element mounted within the housing. The inlet scoop also includes an arrangement for stagnating airflow around the sensor element so that the sensor element may obtain the desired temperature reading. When the housing of the total temperature sensor probe is subjected to icing conditions, ice may form not only on the outer portion of the housing but also in and around the inlet scoop and on the airflow stagnating surfaces. The accumulation of ice alters the airflow around the airflow stagnating surfaces and prevents the surfaces from performing their intended function. This causes erroneous temperature readings by the sensor. Also, ice destroys the desired aerodynamic properties of the remainder of the probe and increases overall weight.
Prior deicing devices for deicing pitot tubes, total temperature probes, and other aerodynamic components included an electrical resistive cable-type heater mounted within the component body and extending in a complex serpentine pattern across every area on the component body in which deicing was desired. The particular component was first cast or otherwise formed with a complex serpentine channel extending across the areas to be deiced, and then the heater element was mounted in the channel. The cable-type heater had to be bent into the desired complex shape, staked or tacked down in the channel, and then the channel had to be filled with a heat conductive braze. Excess braze was finally machined or ground away to complete the desired aerodynamic shape.
Although this cable-type heater deicing arrangement was common in the industry for many years, there were a number of problems associated with such deicing arrangements. First, the time required to carefully bend the heating element, stake it in place, braze it in, and then grind the component, was excessive, easily accounting for 70% of total production time. Thus, the prior deicing arrangement was very expensive in terms of labor cost. Also, the production process resulted in many defective products since the cables were susceptible to damage in the bending and staking process, and were particularly susceptible to damage by the heat to which they were subjected in the brazing process. Even if the cable-type heater survived the bending, staking, and heating, a mistake in the braze grinding process could damage the heater element. In addition to high cost and low yield resulting from the required production process, the heater life in the surface cable-heater deicing arrangement was low due to the poor heat conduction path from the heating element through the electrical insulating material required to electrically isolate the thin elongated heater element from the component body.